The MRI apparatus performs an imaging of an object placed on a table, and acquires internal data of the object as image data.
The MRI apparatus includes a transmission coil, such as a whole body (WB) coil, for transmitting high frequency pulses, that is, radio frequency (RF) pulses. The WB coil receives RF pulse signals from an RF transmitter, and excites atomic nuclear spins of an imaging site placed in the static magnetic field with high frequency pulses of Larmor frequency, that is, the RF pulses. Then, the MRI apparatus receives magnetic resonance signals, that is, MR signals generated from the imaging site with the excitation by a receiving coil, for example a local coil, and generates the image data based on the MR signals.
A transmission line for transmitting the RF pulses is provided between the RF transmitter and the WB coil which is a load of the RF transmitter. The impedance (that is, a load impedance) of the WB coil is set so as to coincide with the characteristic impedance (for example, 50 [Ω]) of the transmission line.
However, the load impedance varies depending on a weight of a patient placed in the WB coil and the imaging site of the patient.